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LTC6990 - TimerBlox: Voltage Controlled Silicon Oscillator

LTC6990 - TimerBlox: Voltage Controlled Silicon Oscillator
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LTC6990 - TimerBlox: Voltage Controlled Silicon Oscillator - 1

LTC6990 1 6990f TYPICAL APPLICATION DESCRIPTION TimerBlox: Voltage Controlled Silicon Oscillator The LTC®6990 is a precision silicon oscillator with a programmable frequency range of 488Hz to 2MHz. It can be used as a fi xed-frequency or voltage-controlled oscillator (VCO). The LTC6990 is part of the TimerBlox™ family of versatile silicon timing devices. A single resistor, RSET, programs the LTC6990’s internal master oscillator frequency. The output frequency is determined by this master oscillator and an internal frequency divider, NDIV, programmable to eight settings from 1 to 128. fOUT = 1MHz NDIV • 50kÙ RSET ,NDIV = 1, 2, 4 …128 Optionally, a second resistor at the SET input provides linear voltage control of the output frequency and can be used for frequency modulation. A narrow or wide VCO tuning range can be confi gured by the appropriate selection of the two resistors. The LTC6990 includes an enable function that is synchronized with the master oscillator to ensure clean, glitch-free output pulses. The disabled output can be confi gured to be high impedance or forced low. The LTC6990 is available in the 6-lead SOT-23 (ThinSOT) package or a 6-lead 2mm × 3mm DFN. Voltage Controlled Oscillator with 16:1 Frequency Range L, LT, LTC and LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. TimerBlox and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6342817, 6614313. FEATURES APPLICATIONS n Fixed-Frequency or Voltage-Controlled Operation – Fixed: Single Resistor Programs Frequency with <2.2% Max Error – VCO: Two Resistors Set VCO Center Frequency and Tuning Range n Frequency Range: 488Hz to 2MHz n 2.25V to 5.5V Single Supply Operation n 72ìA Supply Current at 100kHz n 500ìs Start-Up Time n VCO Bandwidth >300kHz at 1MHz n CMOS Logic Output Sources/Sinks 20mA n 50% Duty Cycle Square Wave Output n Output Enable (Selectable Low or Hi-Z When Disabled) n –40°C to 125°C Operating Temperature Range n Available in Low Profi le (1mm) SOT-23 (ThinSOT™) and 2mm × 3mm DFN Package n Low Cost Precision Programmable Oscillator n Voltage-Controlled Oscillator n High Vibration, High Acceleration Environments n Replacement for Fixed Crystal and Ceramic Oscillators n Portable and Battery-Powered Equipment VCO Transfer Function VCTRL (V) 0 fOUT (kHz) 1000 750 250 500 0 0.5 6990 TA01b 1 1.5 2 6990 TA01a LTC6990 OE GND SET OUT V+ DIV C1 0.1ìF RSET 100k V+ V+ VCTRL RVCO 100k fOUT .. 1MHz .. VCTRL • 0.5 MHz V

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LTC6990 - TimerBlox: Voltage Controlled Silicon Oscillator - 3

LTC6990 3 6990f ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS fOUT Output Frequency Recommended Range: RSET = 50k to 800k Extended Range: RSET = 25k to 800k 0.488 0.488 1000 2000 kHz kHz ÄfOUT Frequency Accuracy (Note 4) Recommended Range RSET = 50k to 800k l ±0.8 ±1.5 ±2.2 %% Extended Range RSET = 25k to 800k l ±2.4 ±3.2 %% ÄfOUT/ÄT Frequency Drift Over Temperature l ±0.005 %/°C ÄfOUT/ÄV+ Frequency Drift Over Supply V+ = 4.5V to 5.5V V+ = 2.25V to 4.5V l l 0.23 0.06 0.55 0.16 %/V %/V Period Jitter (Note 10) NDIV = 1 0.38 %P-P NDIV = 2 0.22 0.027 %P-P %RMS NDIV =...

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LTC6990 - TimerBlox: Voltage Controlled Silicon Oscillator - 4

LTC6990 4 6990f E LECTRICAL CHARACTERISTICSThe l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. Test conditions are V+ = 2.25V to 5.5V, OE = V+, DIVCODE = 0 to 15 (NDIV = 1 to 128), RSET = 25k to 800k, RLOAD = ‡, CLOAD = 5pF unless otherwise noted. Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC6990C is guaranteed...

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LTC6990 - TimerBlox: Voltage Controlled Silicon Oscillator - 7

LTC6990 7 6990f Rise and Fall Time vs Supply Voltage Output Disable Propagation Delay (tPD) vs Supply Voltage TYPICAL PERFORMANCE CHARACTERISTICS Frequency Modulation Frequency Modulation Typical ISET Current Limit vs V+ Typical Output Waveform SUPPLY VOLTAGE (V) RISE/FALL TIME (ns) 6990 G16 3.0 1.5 2.5 1.0 0.5 2.0 0 2 3 4 5 6 TA = 25°C CLOAD = 5pF tRISE tFALL SUPPLY VOLTAGE (V) PROPAGATION DELAY (ns) 6990 G17 50 20 40 10 30 25 45 15 5 35 0 2 3 4 5 6 TA = 25°C CLOAD = 5pF SUPPLY VOLTAGE (V) ISET (ìA) 6990 G18 1000 400 800 200 600 0 2 3 4 5 6 TA = 25°C SET PIN SHORTED TO GND 20ìs/DIV 6990...

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LTC6990 - TimerBlox: Voltage Controlled Silicon Oscillator - 8

LTC6990 8 6990f PIN FUNCTIONS V+ (Pin 1/Pin 5): Supply Voltage (2.25V to 5.5V). This supply must be kept free from noise and ripple. It should be bypassed directly to the GND pin with a 0.1ìF capacitor. DIV (Pin 2/Pin 4): Programmable Divider and Hi-Z Mode Input. A V+ referenced A/D converter monitors the DIV pin voltage (VDIV) to determine a 4-bit result (DIVCODE). VDIV may be generated by a resistor divider between V+ and GND. Use 1% resistors to ensure an accurate result. The DIV pin and resistors should be shielded from the OUT pin or any other traces that have fast edges. Limit the...

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LTC6990 - TimerBlox: Voltage Controlled Silicon Oscillator - 9

LTC6990 9 6990f BLOCK DIAGRAM 6990 BD PROGRAMMABLE DIVIDER ÷1, 2, 4, 8, 16, 32, 64, 128 MASTER OSCILLATOR Hi-Z WHEN DISABLED Hi-Z OUTPUT UNTIL SETTLED POR DIGITAL FILTER 4-BIT A/D CONVERTER R1 Hi-Z BIT R2 DIV V+ OE OUT 5 4 1 6 HALT OSCILLATOR IF ISET < 500nA MCLK + – ISET VSET = 1V +– 1V 2 3 GND SET RSET tOUT tMASTER .. 1ìs 50k.. • VSET ISET (S6 Package Pin Numbers Shown)

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LTC6990 - TimerBlox: Voltage Controlled Silicon Oscillator - 10

LTC6990 10 6990f OPERATION The LTC6990 is built around a master oscillator with a 1MHz maximum frequency. The oscillator is controlled by the SET pin current (ISET) and voltage (VSET), with a 1MHz • 50k conversion factor that is accurate to ±0.8% under typical conditions. fMASTER = 1 tMASTER =1MHz • 50k • ISET VSET A feedback loop maintains VSET at 1V ±30mV, leaving ISET as the primary means of controlling the output frequency. The simplest way to generate ISET is to connect a resistor (RSET) between SET and GND, such that ISET = VSET/RSET. The master oscillator equation reduces to: fMASTER...

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